<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    p {
        text-align: center;
    }
</style>

<body>
    <p> <button>0</button></p>
</body>

</html>
<script>
    var btn = document.querySelector('button')
    btn.onclick = function () {
        alert(btn.innerHTML++)
    }
</script>